How can I rotate particle instances on the X axis?
If you want to make the particles stand up and rotate on the Z axis, choose Orientation Axis &gt; Global Z, as the object is probably not oriented the way you want on the surface, select the original object, go in Edit mode and rotate it correctly. Now play with the Rotation &gt; Random Phase value.
Edit: Your question is not clear, either you want to vary the orientation axis, or you want to keep the same orientation but change the rotation values. For case #1, use the Randomize value, for case #2, use the Randomize Phase value: